Variation in peptide net production and growth among strains of the toxic cyanobacterium Planktothrix spp.

Abstract

Cyanobacteria frequently form mass developments in surface waters. Populations consist of strains that differ in the production of bioactive peptides, e.g. microcystins (MC) inhibiting protein phosphatases 1 and 2A and anabaenopeptins (APN) inhibiting carboxypeptidases. Forty-nine strains (18 green-pigmented (phycocyanin-rich) P. agardhii strains and 31 red-pigmented (phycoerythrin-rich) P. rubescens strains) of the filamentous cyanobacterium Planktothrix (Anagnostidis et Komarék) were analysed for their MC and APN net production rates. These rates were compared with (i) the pigmentation, (ii) the proportion of extra- and intracellular peptide concentrations and (iii) the cellular growth rates under standardized laboratory conditions. Excluding the strains lacking MC and APN, the MC and APN contents varied up to 14-fold and 12-fold, each. The variation in minimum and maximum peptide content (0.32–4.51 µg MC mg−1 dry weight; 0.85–10.32 µg APN mg−1 dry weight) exceeded the variation found for chlorophyll a (4.8–16.9 µg mg−1 dry weight). The extracellular proportions of MC (0–62%) and APN (0–58%) varied among strains, however, on average, proportions of extracellular MC and APN were low (MC: 8.8 ± (1 SE) 1.9%, APN: 8.4 ± 1.8%). Among all strains cellular growth rates showed a 5-fold variation (0.07–0.33 doublings of dry weight.day−1) and were found independent of the pigmentation and the peptide net production rate. It is concluded that the MC and APN net production rate is not causally related to the cell-division cycle and the synthesis of highest amounts of MC and APN does not constrain cell division.